The present invention relates to a method and to an apparatus for applying flowable foamed, pasty or liquid media to workpieces, particularly for applying foamed media to running webs of carpeting or the like.
The pile of a running carpet is normally provided with a coat of ink, dye, cleaning agent, impregnating agent, softening agent, stiffening agent and/or another flowable medium by resorting to an apparatus wherein a squeegee or another suitable applicator applies a relatively narrow or a relatively wide layer of flowable medium transversely of one side of the running workpiece, either directly or through the interstices of a screen. Reference may be had, for example, to commonly owned U.S. Pat. No. 4,055,119 granted Oct. 25, 1977.
A drawback of many presently known apparatus of the above outlined character is that the application of a flowable medium to the workpiece is not uniform under any and all circumstances, for example, that the medium is likely to penetrate deeper into the workpiece than contemplated, that the penetration is less pronounced than desired, that regions of excessive penetration alternate with regions of insufficient penetration, and/or that media having different compositions and/or consistencies cannot be applied with the same degree of predictability and reproducibility. One of the reasons for such lack of predictability in the application of flowable media is that certain portions of the stream or streams of a flowable medium which are caused to flow toward and contact the workpiece are free to flow at a higher speed and/or at a higher pressure than the remaining portion or portions of such streams. This results in more pronounced application of flowable medium to certain portions of the workpiece, not for the purpose of causing the applied medium to impart to the workpiece an eye-pleasing design or pattern but rather as a result of unpredictable irregular application of the medium to the workpiece.
Another drawback of many presently known apparatus for the application of foamed or other flowable media to workpieces is that their applicators are bulky and hence difficult to install, especially if the apparatus comprise screens and the applicators must be installed in the interior of such screens together with their supports and with the means for supplying flowable media thereto.
German Offenlegungsschrift No. 25 23 062 discloses an apparatus wherein the applicator of a foamed treating medium includes an elongated box-like housing and a foam generator which is connected with the housing by a conduit. The housing accommodates a set of sheet metal steps or stairs which are intended to effect a cascading of foam in a direction toward the outlet, i.e., toward contact with the workpiece below the housing. The steps or stairs partially overlap each other and extend transversely of the outlet which is constituted by the open underside of the housing. Such arrangement promotes the distribution of foam in the interior of the housing but is incapable of ensuring predictable or uniform distribution of foam in the region where such treating medium comes, or is about to come, into actual contact with the workpiece. The lowermost step or steps are disposed at a considerable distance from and above the workpiece, and the foam must overflow such lowermost step or steps to thereupon drip onto the workpiece. These lowermost steps are parallel to the plane of the workpiece therebelow. The housing must be filled to a level such that all of the steps are confined in the mass of foam. The lowermost step or steps are supposed to prevent the foam from penetrating therebelow. The just discussed apparatus fails to ensure predictable distribution of a foamed treating medium in immediate or close proximity to the plane or path of the workpiece.
U.S. Pat. No. 2,800,075 discloses a slotted squeegee which cooperates with a screen or stencil and is capable of distributing a flowable treating medium across a reasonably wide workpiece. The outlet of the patented squeegee is not a continuous passage because the squeegee is intended for the making of multicolored patterns. However, many presently known slotted squeegees are provided with continuous slots or outlets for evacuation of a treating medium from their interior. Regardless of the continuity or discontinuity of their outlets, the just mentioned squeegees are incapable of ensuring predictable or uniform distribution of a flowable treating medium, especially foam, across the full width of a reasonably wide or very side workpiece, e.g., a carpet whose width approximates, equals or even exceeds five meters. The squeegee of U.S. Pat. No. 2,800,075 includes an elongated housing which is closed save for the outlet which discharges the treating medium in a direction toward the workpiece. The medium which is confined in the housing can be maintained at or above atmospheric pressure. As a rule, the squeegee is installed in a screen printing machine so that the medium which issues from the housing must penetrate through the interstices of a screen or stencil before it can reach the material of the workpiece, e.g., a web or sheet of textile material which is held and/or advanced in a horizontal plane. The treating medium is admitted into the housing of the squeegee by way of one or more conduits, and the entire squeegee is preferably mounted in such a way that it can be moved to any one of several levels with reference to the plane or path of the workpiece.
A problem which invariably arises when one deals with a foamed treating medium is that the "inertia" of foam is very high. Thus, foam tends to remain in the place to which it is delivered and does not exhibit any, or exhibits only a negligible, tendency to spread out and to establish a horizontal upper surface as is the case with readily flowable and even viscous or highly viscous liquids. The tendency of foam to retain its shape (e.g., to pile up at the locus of admission into the interior of a squeegee) is especially pronounced if the percentage of gaseous fraction therein is relatively high. On the other hand, foams exhibit a number of very important advantages which are especially desirable in connection with the application of accurately metered quantities of liquids to stationary or running workpieces, such as webs of carpeting or other types of textile material. Thus, a relatively small quantity of liquid fraction (such as a dye) can be uniformly distributed in a large mass of foam and, if the foam is uniformly spread over a web or sheet of textile material, each unit area of such material can receive a very accurately metered quantity of liquid fraction, namely, a quantity which could not be distributed with the same degree of accuracy if the liquid fraction were supplied to the location of application without a gaseous carrier medium. In other words, there exists an urgent need for an apparatus which would be capable of effecting uniform or predictable distribution of a foamed treating medium over a stationary or running workpiece because such apparatus could be used with great advantage in screen printing and analogous machines for distribution of small quantities of liquids with a heretofore unmatched degree of accuracy and reproducibility. This is important when a workpiece is to be provided with a coat of uniformly distributed liquid treating medium as well as when such treating medium is to be applied only to selected portions of a workpiece. In dealing with foams, one must further bear in mind that a foam must be processed without much delay because even short-lasting stagnation of foam results in decomposition ahead of the workpiece and in unpredictable distribution of the thus segregated liquid fraction in the freshly admitted foam. This is particularly undesirable if the liquid fraction is or contains a coloring agent because the hue or the color of a workpiece can be altered drastically by the presence of excessive quantities of liquid fraction, especially a liquid fraction which was permitted to interrupt its progress toward contact with the workpiece for a longer interval of time.